The present invention relates generally to a sliver opening device of an open-end spinning unit and, more particularly, to such a sliver opening device having an opening cylinder housing which is fixed on a pivotably mounted cover element of the spinning unit with a soil discharge opening arranged in the direction of rotation of the opening cylinder behind a sliver infeed position.
Such sliver opening devices are known in various designs and are described e.g. in German Patent Publications DE 29 04 841 A1 or DE 32 21 385 A1. As is known, the separation of soil at the opening cylinder housing is an important element in achieving an unobjectionable processing of the fibrous materials in open-end rotor spinning.
Even though the technology of soil separation devices has long been known and appears to be relatively simple, these devices nevertheless can present design difficulties because the devices often react sensitively to changes. Even small modifications to the separation of soil influence the performance not only as regards the amount of soil separated but also the result of spinning on the whole.
As is known and described e.g. in German Patent Publication DE 29 04 841 A1, the sliver fed between a sliver drawing-in roller and a feed trough is separated by the opening cylinder into individual fibers. During this process soil particles are also separated from the fibers to a very great extent. The opening cylinder transports both components over a fiber guide surface into the area of a soil discharge opening. During this transport both the fibers and the soil particles are accelerated by the opening cylinder and by a current of air rotating with the opening cylinder in a very brief time to a high circumferential speed. The massive particles, that is, fibers and soil particles, have the tendency, as a consequence of the centrifugal force acting on them, to leave the circular path tangentially as soon as the mechanical guidance of the fiber guide surface is interrupted, as happens in the area of the soil discharge opening.
In order to prevent spinnable fibers from loosening from the opening cylinder in addition to the soil particles in the area of the soil discharge opening the soil discharge opening also serves as a suction opening for an additional current of air to enter into the opening cylinder housing. This additional current of air is directed onto the opening cylinder, and because the spinnable fibers on the opening cylinder have a relatively large specific surface in proportion to their low mass, this air current acts essentially in the manner of a "pneumatic guide" to hold the spinnable fibers firmly on the opening cylinder. Soil particles, on the other hand, which have a distinctly greater kinetic energy on account of their greater mass, overcome this air current and are cast off tangentially. In such devices the quality of the cleaning, that is, the quantity of the cleaned-out trash particles as well as the loss of useable fibers, is dependent to a great extent on the correct intensity and the direction of this additional current of air.
The known sliver opening devices, such as described e.g. in German Patent Publication DE 29 04 841 A1, have proven satisfactory in practice. However, occasional problems can occur during operation in sliver opening devices designed in this manner which can be traced back to an incomplete opening of the sliver. That is, there is the danger in the known sliver opening devices that the supplied sliver gradually widens during operation to the point of finally extending laterally beyond the area of the opening cylinder clothing into the area of the side flanges of the opening cylinder, which side flanges limits the opening cylinder clothing. In this instance, fiber clumps can detach from the sliver in an uncontrolled manner, which subsequently results in yarn errors or yarn breaks.
In order to prevent the sliver from being able to turn aside into the area of the side flanges, it has been attempted to lower the side flanges of the opening cylinders behind corresponding wall parts of the opening cylinder housing. German Patent Publication DE 32 21 385 A1 shows a device designed in this manner. As a result of the lowered mounting of the opening cylinder side flanges, the shifting of the sliver into these areas can be avoided. However, the lowered mounting of the opening cylinder side flanges results in a distinct reduction of the width of the soil discharge opening.
Since a vacuum must prevail in the rotor housing of an open-end spinning unit during the spinning process, it is necessary to constantly remove a certain amount of air by suction. The reduction of cross section in the area of the soil discharge opening results in an increase of the rate of flow of the additional current of air entering the opening cylinder housing. This increase of the rate of flow results, in turn, in problems in separating out relatively light trash particles since they are unable to overcome the relatively stronger additional current of air entering the opening cylinder housing. The area at the lower edge of the soil discharge opening is particularly critical since the soil particles in this area have already lost a large part of their kinetic energy so that there is the danger that the light trash particles may be completely braked by the opposing air current and may be subsequently transported back to the opening cylinder.